Plasma etch and deposition processes have become the dominant pattern transfer means used in semiconductor manufacturing over the past 20 years. Most plasma based processes employ the fundamental principle of disassociation of a feed gas by the application of radio frequency (RF) power. As with all plasma loads, one of the dominant characteristics of the plasma load is its non-linearity. The non-linearity of the load affects the voltage and current sine waves of the delivered RF power by creating prevalent harmonic distortion. The exact amount of harmonic distortion, as represented by the amplitude of the harmonic frequencies and the associated phase angle of the current harmonic relative to the corresponding voltage harmonic, is unique to the plasma creating them. To be more precise, the plasma parameters, including ion and electron densities and energies, collision frequencies, neutral constituents, and their respective densities all contribute in a unique way to the amplitude of specific harmonic components of the fundamental frequency applied by a power delivery source to achieve the desired disassociation and subsequent process results.
It is thus apparent that, by monitoring the harmonic components of the fundamental frequency applied by a power delivery source, enhanced process control of plasma deposition and etch processes may be obtained. Consequently, several products have been developed that are designed to provide enhanced process control by monitoring such RF harmonic content. Unfortunately, wide scale proliferation of this technology has not been realized due to several fundamental limitations in the available technology.
One of the most significant limitations in the existing technology has to do with product architecture. To date, several devices are known for monitoring the harmonic content of delivered RF power. Each of these devices requires precise calibration of its individual components. Original hardware designed for plasma process control RF sensors in existing solutions has been based on either: a) RF switch routed band pass filters; (b) directional couplers; or (c) heterodyne or digital signal processor circuitry enabled with programmable local oscillators. Each of these designs comprises a transducer package, commonly located at the point of measurement, and a corresponding analysis and communications electronics package, which is typically located remotely from the point of measurement.
Since each transducer package provides a unique output, these two packages are specifically calibrated to work with each other. Consequently, it is not possible to replace either package independently of the other without recalibrating the system. Since downtime is extremely expensive in a semiconductor processing line, the need for recalibration creates serious maintenance and support issues for users of these RF sensor based process control solutions. Consequently, a need exists in the art for methods and devices that will support a field replacement strategy that allows any transducer package to function properly with any corresponding analysis and communications package, without degradation in performance and without the need for recalibration.
A further issue with existing devices for monitoring the harmonic content of delivered RF power in semiconductor processing has to do with the detector circuits that can be used with these devices. In particular, existing devices, such as those described in U.S. Pat. No. 5,770,992 (Waters), U.S. Pat. No. 5,565,737 (Keane), U.S. Pat. No. 6,046,594 (Mavretic), U.S. Pat. No. 5,808,415 (Hopkins) and U.S. Pat. No. 6,061,006 (Hopkins), all rely on AC coupled voltage and current measurements of the delivered RF power which serve as input signals to frequency discriminating detection circuits for harmonic analysis. Such a configuration places limitations on the detector circuits that can be used to analyze the broadband, harmonically distorted RF signals. Moreover, these devices require interface electronics to process the sampled signals before use in any subsequent application. Also, each of these devices is configured such that the transducer package and associated analysis or interface electronics package are calibrated together and cannot be separated without failure or degradation in overall performance. The shortcomings of such a configuration have been discussed above. There is thus a need in the art for a device for monitoring the harmonic content of delivered RF power that overcomes these deficiencies.
Another issue relating to RF power supplies for plasma reactors concerns the diagnosis of the components of an RF power delivery network. Semiconductor manufacturing facilities are extremely expensive to construct and operate. Consequently, every effort is made to minimize manufacturing tool down time, and maintenance and recovery of an off-line tool is always under excessive time constraints. Often, when a tool is taken off-line due to a failure to meet performance specifications, repair efforts suffer from a lack of diagnostics. Consequently, such repair efforts often become extremely expensive.
FIG. 1 shows a typical configuration for such a system. The system 100 comprises an RF generator 101, an impedance matching network 130, and a load 150. Generator 100 is coupled to impedance matching network 130 through a known impedance 120. This impedance is typically a nominal characteristic value, such as 50 ohms. Impedance 120 serves to facilitate optimal power transfer from the generator to matching network 130. The impedance 140 seen between matching network 130 and load 150 is generally unknown and varies over time.
Most RF power generators have “built-in” output measurement capability, but this is typically located remote from the impedance matching network. Measurement of input power at the input of the impedance matching network has historically been provided by utilization of bolo-meters, calorimeters, diodes and other types of instrumentation. Examples of prior art methods for making RF power measurements in coaxial environments may be found in U.S. Pat. No. 4,547,728 (Mecklenburg), U.S. Pat. No. 4,263,653 (Mecklenburg) and U.S. Pat. No. 4,080,566 (Mecklenburg), all of which rely on an inductive coil design to sample the RF voltage. However, since the measurement to be performed is typically diagnostic and only necessary during maintenance and troubleshooting, the cost, portability and ease of installation are of paramount concern.
Typical prior art methods for measuring the power at the output of the impedance network rely on alternating current (AC) coupled voltage and current measurements of the RF power delivered to the load. These measurements are input to frequency discrimination circuitry for the purpose of performing harmonic analysis. Examples of prior art methods for monitoring components for delivering RF power in semi-conductor processing are described in numerous patents, including, for example, U.S. Pat. No. 5,770,992 (Waters), U.S. Pat. No. 5,565,737 (Keane), U.S. Pat. No. 6,046,594 (Mavretic), U.S. Pat. No. 5,808,415 (Hopkins) and U.S. Pat. No. 6,061,006 (Hopkins). These systems also comprise a transducer package and associated analysis or interface electronics package which are calibrated together, and thus have the infirmities noted above (that is, they cannot be separated without degradation in overall performance).
Traditional RF power measurement technologies offer solutions in either the characteristic impedance portion of the delivery network or the non-characteristic impedance section without any integration of the two measurement devices. Some attempts have been made to integrate expensive and difficult to install frequency discriminating RF sensors, but these have met with poor acceptance due to price and installation issues. There is thus a need in the art for a means for field engineers to quickly, easily, cheaply and accurately diagnose the components of the RF power delivery network and determine which, if any, components of the system are faulty.
The above noted needs are met by the devices and methodologies disclosed herein and hereinafter described.